线程同步技术

（1）互斥对象：函数CreateMutex。在多核下工作不正常。
（2）事件对象：函数CreateEvent、SetEvent、ResetEvent、WaitForSingleObject，应当使用自动重置的事件对象。在多核下工作正常。
（3）关键代码段：类CRITICAL_SECTION，函数InitializeCriticalSection、DeleteCriticalSection、EnterCriticalSection、LeaveCriticalSection。在多核下工作基本正常，但是会出现：“"xxx"指令引用的"xxx"内存。该内存不能为"written"。”。需要注意线程死锁问题。

三者比较：
互斥对象和事件对象都属于内核对象，速度较慢。但可以在多个进程中的各个线程间进行同步。
关键代码段工作在用户方式下，同步速度较快，但容易进入死锁状态，因为在等待进入关键代码段时无法设定超时值。通常，首选关键代码段。
其使用也比较简单，如果在MFC中的话，可在构造函数调用InitializeCriticalSection，在构造函数调用DeleteCriticalSection，在所需保护的代码前调用EnterCriticalSection，在访问完所需保护的资源后调用LeaveCriticalSection即可。

 

----------------例子：互斥对象------------------------------------------------

#include <windows.h>#include <iostream.h>int index=0;int tickets=20;HANDLE hMutex;DWORD WINAPI Fun1Proc(LPVOID lpPrama){while(TRUE){WaitForSingleObject(hMutex,INFINITE);if (tickets>0){Sleep(1); cout<<"thread 1 sell ticket: "<<tickets--<<endl;}else{break;}ReleaseMutex(hMutex);}return 0;}DWORD WINAPI Fun2Proc(LPVOID lpPrama){while(TRUE){WaitForSingleObject(hMutex,INFINITE);if (tickets>0){Sleep(1);cout<<"thread 2 sell ticket: "<<tickets--<<endl;}else{break;}ReleaseMutex(hMutex);}return 0;}void main(){HANDLE hThread1;HANDLE hThread2;hThread1=CreateThread(NULL,0,Fun1Proc,NULL,0,NULL);hThread2=CreateThread(NULL,0,Fun2Proc,NULL,0,NULL);CloseHandle(hThread1);CloseHandle(hThread2);hMutex=CreateMutex(NULL,FALSE,NULL);Sleep(1000);}

正确的结果是由20递减到1，但是本程序会出现以下错误结果：
thread 1 sell ticket: 20
thread 1 sell ticket: 20
thread 2 sell ticket: 19
thread 1 sell ticket: 18
...
thread 2 sell ticket: 1
----------------------------------------------------------------------------------

 

----------------例子：事件对象------------------------------------------------

#include <windows.h>#include <iostream.h>int tickets=20;HANDLE g_hEvent;DWORD WINAPI Fun1Proc(LPVOID lpPrama){while(TRUE){WaitForSingleObject(g_hEvent,INFINITE);//ResetEvent(g_hEvent);if (tickets>0){Sleep(1); cout<<"thread 1 sell ticket: "<<tickets--<<endl;SetEvent(g_hEvent);}else{SetEvent(g_hEvent);break;}}return 0;}DWORD WINAPI Fun2Proc(LPVOID lpPrama){while(TRUE){WaitForSingleObject(g_hEvent,INFINITE);//ResetEvent(g_hEvent);if (tickets>0){Sleep(1); cout<<"thread 2 sell ticket: "<<tickets--<<endl;SetEvent(g_hEvent);}else{SetEvent(g_hEvent);break;}}return 0;}void main(){HANDLE hThread1;HANDLE hThread2;g_hEvent=CreateEvent(NULL,FALSE,FALSE,NULL);SetEvent(g_hEvent);hThread1=CreateThread(NULL,0,Fun1Proc,NULL,0,NULL);hThread2=CreateThread(NULL,0,Fun2Proc,NULL,0,NULL);CloseHandle(hThread1);CloseHandle(hThread2);Sleep(1000);CloseHandle(g_hEvent);}

 

----------------例子：关键代码段---------------------------------------------

//<QA>注释掉两个Mark的代码行后，出现内存不能写异常。#include <windows.h>#include <iostream.h>int tickets=20;CRITICAL_SECTION g_cs;DWORD WINAPI Fun1Proc(LPVOID lpPrama){while(TRUE){EnterCriticalSection(&g_cs);Sleep(1); //Markif (tickets>0){Sleep(1); cout<<"thread 1 sell ticket: "<<tickets--<<endl;LeaveCriticalSection(&g_cs);}else{LeaveCriticalSection(&g_cs);break;}}return 0;}DWORD WINAPI Fun2Proc(LPVOID lpPrama){while(TRUE){EnterCriticalSection(&g_cs);Sleep(1); //Markif (tickets>0){Sleep(1); cout<<"thread 2 sell ticket: "<<tickets--<<endl;LeaveCriticalSection(&g_cs);}else{LeaveCriticalSection(&g_cs);break;}}return 0;}void main(){HANDLE hThread1;HANDLE hThread2;hThread1=CreateThread(NULL,0,Fun1Proc,NULL,0,NULL);hThread2=CreateThread(NULL,0,Fun2Proc,NULL,0,NULL);CloseHandle(hThread1);CloseHandle(hThread2);InitializeCriticalSection(&g_cs);Sleep(1000);DeleteCriticalSection(&g_cs);}